Posted by: Mark Foreman | March 13, 2018

The Novichok agents

Dear Reader,

Things have become more complex, it has been claimed in the UK that the nerve agent attack involved a so-called novichok agent. Now I can not claim to know where these novichok agents came from, who did it or even if a novichok agent was used. I would rather not get sucked into a debate about who did it, I am mainly going to consider the chemistry.

However I can consider some of the chemistry, according to the internet the novichok agents were invented in the Soviet Union in an attempt to make chemical warfare agents even worse than sarin and VX. On Wikipedia it is claimed that methyl-(1-(diethylamino)ethylidene)phosphoramidofluoridate and 1-chloropropan-2-yl (E)-(((chlorofluoromethylene)amino)oxy)phosphonofluoridate are examples of novichok agents.

1-chloropropan-2-yl (E)-(((chlorofluoromethylene)amino)oxy)phosphonofluoridate

Part of the problem is that very little if anything has been written in the academic literature about novichok agents, well at least under that name. I did a search of the web of science and I did not find any mention of any paper with that word in the topic or title on the subject of chemical warfare. On the other hand I found almost 800 papers which have the word “sarin” in the title.

I also looked for methyl (E)-(1-(diethylamino)ethylidene)phosphoramidofluoridate in the organic chemistry literature using one common database, and I could not find any mention of this substance. Looking at it as a organophosphorus chemist I can see that it has the correct groups attached to a phosphorus atom to act as an acetylcholinesterase inhibitor. I also see an electron releasing group which would reduce the partial positive charge on the phosphorus atom when it is compared with sarin. This reduction in partial positive charge would reduce the rate at which the substance will react with water. This change would be likely to make the substance more able to persist in the environment.

However when you look for 1-chloropropan-2-yl (E)-(((chlorofluoromethylene)amino)oxy)phosphonofluoridate you can find plenty written on the subject in the Soviet chemical literature back in the 1960s and 1970s. By reacting dichlorofluoro(nitroso)methane with a phosphorus(III) compound a reaction similar to the Arbuzov reaction occurs which forms the product. Here is my best effort for the mechanism by which the compound is formed.


I hold the view that while the Soviets are thought to have developed the novichok compounds it would not be very hard for a competent (and well protected) phosphorus chemist to make a moderate amount of one of these rather exotic substances. So unlike polonium-210 (which is only produced) in very few nuclear reactors it is impossible to argue based on the identity of the nerve agent where it came from.

One of the problems in life is that sometimes bad people will choose tools or methods which are not normally used by people from their country in an attempt to confuse any investigator. For example the NKVD used German pistols to murder Polish officers at Katyn. This offers some degree of plausible deniability. Thus I think some other evidence other than the identity of the nerve agent is required before anyone can blame anyone for the horrible event which has just occured.



  1. You mentioned that “methyl (E)-(1-(diethylamino)ethylidene)phosphoramidofluoridate” didn’t turn up any references in a common database. However, a ethyl version with almost-identical syntax “Ethyl [(1E)-1-(diethylamino)ethylidene] phosphoramidofluoridate” yields A-234 at chemspider

    The entry for A-232 produces a methyl version of this expression as “Methyl [(1E)-1-(diethylamino)ethylidene]phosphoramidofluoridate” with negligible syntactical differences from your search expression. Odd that Google didn’t find it. Even more oddly, Google doesn’t find the chemspider methyl formula when the exact expression is entered, but does find the ethyl expression.

    My chemistry knowledge is very limited. Ellison’s HAndbook of Chemical and Biological Warfare Agents distinguishes between GV-series nerve agents (alkyl phosphoramidofluoridates) and carbonimidic phosphorohalides (Novichoks). As I read the formulas, A-232 and A-234 are a variation of alkyl phosphoramidofluoridates, but are not novichoks under Ellison’s definition.

    In Mirzayanov’s book (Table 2), he listed A-230 and A-232 as “Novichok precursors”, but not as actual novichoks.

    If the Skripal poison is A-234, as reported in some articles, would it be more accurate to term this as a GV-series nerve agent, rather than a Soviet Novichuk. (Perhaps accounting for its non-lethality thus far).

    A 1957 text by Bernard Saunders described some simple alkyl phosphoramidofluoridates (as early as 1943), referring to the existence of “other compounds in this series” that were “much more toxic”. AS someone looking at formulas with no even shallow experience, A-232 and A-234 look like they would plausibly fit in Saunders’ series. Does this make any sense?

    • The problem with Chemspider is that it contains a lot of things which it has predicted properties for, thus the inclusion in there does not mean it exists. For example I just searched it for cyclobutadiene and it offers properties for macroscopic amounts of a substance which is known to be very unstable. It reacts with itself to form C8H8 so quickly it is impossible to isolate the pure substance. I also found predicted properties for Dewar benzene which is another super unstable substance.

      I used a search of Reaxys, which is database which is of things which have been made in real life.

      Part of the problem with the Novichoks is that there is very little hard information in the literature. One set of strucutures come from a book by a insider who decided to go public about it. The Russians have never formally confirmed that this man got the strucutres right. I suspect that they will always refuse to confirm or deny.

      I think that it may be like VX that the people who made it would rather not release the strucutural formula of the substance.

      Also the different molecules suggested all fit the profile of things which would be able to act as acetylcholinesterase inhibitors which adds to the confusion.

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